We have developed methods for dissection of each defined nephron segment from rat and rabbit kidneys and assays of adenylate cyclase activity, cyclic AMP levels, substrate oxidation, and vitamin D3-1 alpha-hydroxylase in these defined nephron segments. We proposed to extend our study and evaluate the effects and interactions of various key ions and hormones on renal tubular cell metabolism and its relationship to tubular function utilizing these methods in different nephron segments. These studies will shed new light on our understanding of the ionic and hormonal control of renal cell function and metabolism.